Advanced wireless communication systems, such as multiple-input multiple-output (MIMO) communication systems, increasingly rely upon concurrent signal transmissions from multiple antenna subarrays of an antenna array to form desired radiation patterns. An antenna subarray may be made of one or more antenna elements. Theoretically, by altering the signal characteristics of concurrently transmitted signals, such as by altering the phase or magnitude of the concurrently transmitted signals, one or both of lobes and nulls may be formed in desired locations. On transmission, radiation pattern lobes are desirable to focus energy at a location of a receiver, and nulls are desirable to reduce the interference seen by other receivers. When receiving, a lobe can increase the signal strength of a desired transmitter, and a null may eliminate interference from a non-desirable transmitter.
Multiple real-world factors, referred to herein as antenna impairments, may affect the ideal, or theoretical, transmission characteristics of an antenna array. Such impairments may include, but are not limited to, differences in the signal paths between the transmitters and the antenna subarrays of the antenna array, mutual coupling between antenna subarrays, ground plane imperfections, mechanical tolerance differences, differences in radio equipment hardware, and the like. Impairments alter the ideal, or theoretical, antenna radiation pattern characteristics and therefore affect the ability to accurately place a lobe or null where desired. Such impairments may result in lower system throughput.
Substantial efforts are often put into antenna design to eliminate or minimize some impairments, such as mutual coupling between antenna subarrays. This increases the design cost and extends the design time of an antenna array. Frequently, design changes that are implemented to avoid impairments, such as mutual coupling, result in performance tradeoffs. Alternatively, the effects of mutual coupling may simply be ignored, resulting in non-ideal radiation patterns. As wireless bandwidth and system throughput becomes increasingly valuable, it becomes increasingly important to accurately form radiation patterns as desired.